If your belt ends aren't swinging while u are punching then you probably aren't getting the full power transfer.

We are all taught to punch and kick through the target for optimum power.

Also remember that as you punch with one fist you are automatically torqueing / loading up the other fist [via the body mechanics] for a hard hit if you are doing it properly. Hence why your right cross will hit harder than the left jab in a jab/cross combination.

A 3/4 twist punch will provide most power transfer provided you can hit properly with the top of the 1st 2 knuckles on the horizontal. Keep your wrist straight so that the alignment is along the 2 bones of the forearm and that they are not twisted..